How to emulate D365 client for smartphone in Chrome

With D365 v9.0 Microsoft introduced Unified User Interface. The mobile clients for tablet and smartphone now only use UUI.
Recently Microsoft provided Service Update 6 for D365 v9.0 and now I’m able to open D365 in Dynamics 365 app on my smartphone successfully.

But sometimes you maybe have no smartphone available or just want to check some customizations in your browser how they look like on the smartphone. Especially with the introduction of Custom Control Framework (CCF) I suppose this will be required more often.
Before v9.0 there was a specific URL available to open the mobile client for tablets or phone in the browser. With v9.0 this URL is no longer working.

But there is a simple approach for Chrome and I suppose a quite similar approach for other browsers as well.

This approach will not replace functional tests with a real device but it can speed up customizing activities. You only need to think about the different layout possibilities for web, tablet and phone provided by CCF.